1. Technical Field
This invention relates to novel polymer blend compositions which are excellent in fluidity, heat resistance and mechanical characteristics.
2. Background Art
Thermoplastic resins having well-balanced fluidity, heat resistance and mechanical characteristics are generally needed for industrial purposes.
For example, polyphenylene ether resins are excellent in mechanical characteristics, electrical properties, acid-resistance, alkali-resistance, heat resistance, etc. and have low water absorbing capacity and high dimensional stability. Because of having these properties, polyphenylene ether resins have been widely employed as, for example, housing chassis materials in electrical apparatuses and office automation (OA) instruments such as computers and word processors. Moreover, it is frequently required that these materials be flame retarding from the viewpoint of fire prevention. With the recent remarkable progress in the technology, OA instruments have become more and more small-scaled and lightweight with improved functions. Thus, these materials are frequently molded into thin-walled articles. Therefore, it has been desired to further improve the fluidity (molding proccessability) of these resin materials.
Because of its poor fluidity, polyphenylene ether is generally employed in the form of polymer blends with polystyrene, as suggested by JP-B-43-17812 (the term "JP-B" as used herein means an "examined Japanese patent publication") and U.S. Pat. No. 3,383,435. Polyphenylene and polystyrene are compatible with each other completely at an arbitrary ratio. As the polystyrene content increases, the fluidity is improved but the heat resistance is lowered. Although JP-B-48-40046 discloses mixtures of a polyphenylene ether with a styrene/acrylonitrile copolymer containing from 3 to 18% by weight of the acrylonitrile component, these compositions are not necessarily satisfactory in the balance of heat resistance, fluidity and mechanical characteristics.
Further, JP-A-6-306254 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a technique for improving the balance of heat resistance and fluidity by using an acrylonitrile/styrene resin containing a specific amount of acrylonitrile. However, this technique suffers from a problem that peeling phenomenon of the resin is not sufficiently controlled and has a poor practical strength.
Furthermore, JP-A-9-31321 discloses a technique for improving the fluidity of a resin composition by blending a polyphenylene ether, a polystyrene and/or rubber-modified polystyrene with a styrene/acrylonitrile copolymer having an acrylonitrile content of from 7 to 11% by weight and a melt flow rate of from 5 to 100 g/10 min. Although the fluidity can be improved thereby, the impact strength and heat distortion temperature are lowered with a decrease in the molding temperature.